From "Living with Chickens" by Jay Rossier:
"When a hen begins laying, the minerals that produce the yellow pigment on her legs and in her beak and other areas is diverted to the yolks of the eggs, and the color slowly drains from the pigmented parts of her body."
I am new to chickens but I was amazed when I read that! I had no idea! Could this be what's happening to your girl?